Generally, concrete obtained by combining aggregate by cement is used as a civil-engineering material and construction material. The sulfur recently receives an attention due to the characteristics that the sulfur is a solid at room temperature while melted upon being heated to about 119° C. to 159° C., and it is attempted that the sulfur is utilized as a civil-engineering material and a construction material by mixing a predetermined sample or predetermined samples in it. It is known that the sulfur-containing material using the sulfur has high strength, an excellent water-sealing property and high acid resistance, as compared with usual concrete employing cement. Further, since the sulfur-containing material is apparently similar to a usual concrete in finishing and handling, sometimes the solidified material is called sulfur concrete substance.
Since the sulfur has ignition property and is dealt with a hazardous material, it is difficult to perform construction by melting, casting and solidifying the sulfur material on site. Therefore, in order to improve such a situation, it is attempted that the sulfur is denatured to produce modified sulfur by mixing a sulfur modifying agent as an additive into molten sulfur. Further, it is attempted that a modified sulfur intermediate material in a melt state is produced by mixing the modified sulfur and fine powders, and a modified sulfur concrete substance is produced by mixing the modified sulfur intermediate material with the aggregate and solidifying the mixture.
Further, in order to form the sulfur concrete substance or the modified sulfur concrete substance by making the sulfur-containing material (or the modified sulfur intermediate material) in the melt state cooled and solidified, the sulfur containing material is injected into a mold having a predetermined shape, and thereafter, is cooled and solidified.
As a technique of producing a sulfur-concrete product which can be immediately removed from the mold after hermetic sealing and has a smooth surface and excellent durability, a technique is disclosed in which a mixture obtained by mixing from 1 to 20 volume parts of mineral fine powders to 1 volume part of the sulfur is heated to the melting point of sulfur or higher and hermetically sealed, thereby forming a compact having self molding performance.
However, the sulfur-containing material in the melt state start to solidify at the time point when the temperature is below solidification temperature (about 119° C.) of the sulfur and solidifies to have high strength which is equal to or higher than that of usual concrete. Conventionally, when the sulfur-containing material in the melt state solidifies, a part which is in contact with the mold when the material is poured into the mold is cooled rapidly, so that a problem occurs such that the surface of the sulfur concrete substance or the modified sulfur concrete substance removed from the mold is rough. In addition, it is difficult to manufacture a product having high precision in shape.
Furthermore, when a cylindrical product such as a hume pipe or a manhole is manufactured by usual concrete, a producing method called centrifugal molding of injecting the concrete into a cylindrical mold while rotating and vibrating the mold so as to press the material against the inner peripheral surface of the mold by centrifugal force and vibration is employed. In this case, a skilled hand is needed for finishing of the inner peripheral surface of the cylindrical product, and it takes long time. First of all, since the sulfur-containing material in the melt state start to solidify at the time point when the temperature is below the solidification temperature (about 119° C.) of the sulfur, a product may not be manufactured by using the centrifugal molding of pressing the material against the inner peripheral surface of the mold by using the centrifugal force.